1. Field of the Invention
This invention generally relates to worm shaft attachment structures. More specifically, the present invention relates to worm shaft attachment structures, in which a worm shaft is attached rotatably to a reel unit via first and second bearings that are disposed at the two ends of the worm shaft, wherein intersecting helical grooves are formed on an outer circumferential surface of the worm shaft, and the worm shaft is for reciprocating a spool back and forth in cooperation with a rotation of a handle, the spool being for winding line on a spinning reel.
2. Background Information
Typical spinning reels include a reel unit, a rotor rotatably supported by the reel unit, and a spool around which fishing line can be wound. The rotor has a pair of arm portions. Between the two arm portions, a bail is provided that can be switched between a line-winding posture and a line-releasing posture. Furthermore, a line roller for guiding fishing line to the spool when winding up line is provided at the front end of one of the arm portions.
Such spinning reels are provided with an oscillation mechanism for winding fishing line that is guided by the bail and the line roller, uniformly in horizontal direction relative to the spool. This oscillation mechanism is disposed inside the reel unit, and includes a worm shaft that is arranged parallel to the spool shaft on which the spool is mounted, a transmission mechanism that lets the worm shaft rotate in cooperation with the rotor, and a slider engaging the worm shaft.
Intersecting helical grooves are formed on the outer periphery of the worm shaft, and the worm shaft is supported rotatably by the reel unit via two bearings mounted to both ends. An intermediate gear for transmitting rotation from a pinion gear to the worm shaft is mounted non-rotatably to the front of the worm shaft.
Conventionally, the rear end of the worm shaft is supported via a bearing by a rear wall portion formed at the rear of the reel unit. A through hole through which the worm shaft can pass is formed in the rear wall portion, and the front end of the worm shaft is supported by the reel unit via a bearing mounted to that through hole. Furthermore, the front end of the worm shaft is supported via a bearing by a concave hole formed in the front of the reel unit. When attaching such a worm shaft to a reel unit, the front end of the worm shaft is inserted from behind the reel unit through the through hole on the rear end side, while the bearing is mounted to the concave hole on the front side, and after the intermediate gear is mounted at the front, the front end of the worm shaft is mounted to the bearing mounted in the concave hole. Then, a bearing is fitted in the through hole on the rear end side, and a locking plate preventing the bearing from falling off is mounted to the rear face of the rear wall portion, thereby finalizing the operation of attaching the worm shaft.
With this oscillation mechanism, the slider is shifted back and forth along the worm shaft while engaging helical grooves in the worm shaft, which rotates in cooperation with a rotation of the handle. By shifting the slider back and forth along the worm shaft, the spool shaft and the spool can also be shifted back and forth. Thus, fishing line can be wound uniformly around the spool by shifting the spool back and forth in cooperation with the rotation of the handle and in synchronization with the rotor.
With the worm shaft attachment structure of the conventional configuration as described above, the through hole formed in the rear wall of the reel unit and the concave hole formed in front are formed individually in the back and the front. For this reason, if the reel unit is retrieved from the die in lateral direction when forming the reel unit by die forming using a fixed die, such as die casting or injection molding, then the through hole and the concave hole have to be formed with special sliding dies that slide back and forth and are provided separately from the fixed die. If the through hole and the concave hole are formed using such special sliding dies, then the sliding dies may be shifted out of position during the molding even if they are arranged concentrically with high precision. For this reason, it is difficult to form the concave hole and the through hole concentrically with high precision, and it is hard to maintain the attachment precision of the worm shaft. In particular in the case of large spinning reels, the length of the worm shaft becomes long, so that it becomes difficult to ensure the precision.
Furthermore, since the worm shaft is mounted from the rear, if a separate outer peripheral portion of the reel unit is formed behind the rear wall portion, then it is necessary to provide the outer peripheral portion with a through hole for passing through the worm shaft. And forming such a through hole may restrict the design options for that portion.
In view of the above, there exists a need for a worm shaft attachment structure for a spinning reel, which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.